One is the release from a UK publisher (the more expensive). The other is the release from a US publisher.
The UK one, with a higher page count, must have tighter margins or different font. (Or some of the data could be wrong, maybe cross check the isbn numbers on Amazon?)
It's not that unusual for a novel to be in different formats for different markets based on the publishers. Like when the first of these novels came out it was a full size hardcover in one market and a small paperback in others.
The UK one might also have all the "u"a back in words like honour and colour.